In a xenon chloride excimer laser, an electric glow discharge causes hydrogen chloride and xenon gases to react, and excites the resulting xenon chloride, XeCl, so that it lases. As the laser operates, its power gradually diminishes. When the loss of power renders the laser unsuitable for its intended use, the gases in the lasing chamber must be replaced with fresh hydrogen chloride and possibly xenon. This is frequently inconvenient and requires a costly shutdown of the laser.